Method of modulating high frequency transmitters



June 6, 1939.

I PUNGs 2,161,313

METHOD OFI MODULATING HIGH FREQUENCY TRANSMITTERS Filed Feb. 20, 1937 INVENTOR 0 PVA/6K9 ATTORNEY Patented June 6, 1939 PATENT OFFICE METHOD F MODULATING HIGH FRE- QUENCY TRANSMITTERS Leo Pungs, Brunswick, Germany Application February 20, 1937, Serial No. 126,805 In Germany February 21, 1936 2 Claims.

It is well known to subject high frequency carrier waves to a multiple modulation by modulating intermediary carriers with the signals to be transmitted, such intermediary carriers in their 5 turn serving to modulate the high frequency carrier proper. Owing to the use of intermediary carriers the signal frequency bands shall be located aside each other or an ultra-short carrier wave, for instance, shall be. utilized in a multii'old manner.

The invention proposes to employ the method of the so-called carrier adaptation which is known to consist in displacing the working point along the modulation characteristic. In this connection a direct voltage is derived from the modulating currents in order to displace the working point in dependence on the mean value of the modulation amplitudes and in such a manner that the lowest possible energy losses shall occur.

The method of displacing the working point along the modulation characteristic and in dependence upon the mean value of the modulation amplitudes is well known per se but has not been employed so far in connection with a multiple modulation. According to the present invention,

however, this known method of carrier adaptation is applied to a multiple modulation system and is so applied as to control the mean level of the intermediary carriers.

The preferred arrangement for carrying out the method of the present invention is schematically represented in the single figure of drawing. In this drawing all the apparatus shown in light lines represents a multiple modulation system of conventional type. The connections shown in heavy lines represent the additional apparatus which must be added for carrying out the method of the present invention.

As shown in the drawing, a generator I is provided for producing oscillations which are modulated in device 2 and then transmitted through coupling device 3 to radiating antenna 4. The modulation in device 2 is controlled by the signal input from two modulating assemblies designated generally by the reference characters 5 and 6. As shown in the drawing,modulating assembly 5 comp-rises an intermediate frequency generator I0 for producing an intermediary carrier frequency, a modulating device II for modulating this intermediary carrier frequency, a signal source I2 for controlling said modulation of the intermediary carrier and a modulation amplifier -I3 for amplifying the controlling signal to a suitable level for controlling the modulations. 'Ihe second modulating assembly 6 is exactly similar to the first modulating assembly 5. The outputs from'both of these modulating assemblies 5 and 6 are transmitted to modulating device 2 for controlling the modulation of the high frequency oscillations from generator I. 5 So far the apparatus described represents merely the known type of multiple modulation system.' For carrying out the novel method of the present invention the additional equipment shown at I5 and 25 is added. If the modulation 10 amplifier I3 is of a type which inherently delivers a direct current component of approximately the desired characteristic, this direct current component may be simply conducted to suitable input terminals of modulation device II by 15 means of a transmission channel such as I5. For example, if a directly proportional variation of the intermediate carrier with respect to the average modulating amplitude is desired, and if the amplier I3 inherently produces a direct current 20 component which is proportional to the modulating amplitude, the additional equipment may consist as shown, of a simple transmission line joining the amplifier I3 with the modulating device II. On the other hand, if the amplifier I3 25 does not produce a direct current component of the desired form additional means should be included for producing such a current. Means of this type are well known in the art and need not be described in detail. Conventional recti- 30 fying means can be used for producing the desired direct current. In fact, it is already well known how to control a carrier in accordance with the mean amplitude of a modulating signal and therefore the complete assembly 5 may be 35 itself considered as a well known system modified so as to deliver an intermediate frequency carrier at a level suitable for modulating instead of delivering a high frequency oscillation at a level suitable for radiation. 40

The use in accordance with my invention of the above described method for controlling the intermediary carriers in the case of multiple modulation provides the following advantages. The high modulation amplitudes of the different sig- 45 nals to be transmitted will not occur at the same time but at different times. As is well known a disadvantage of multiple modulation is that the energy is apportioned to the several intermediary carriers, that is to say, the larger the 50 number of intermediary carriers employed, this being equivalent to the number of the signals to be transmitted, the lower is the amount of energy available for each channel of the high frequency carrier. 'Ihe use of the method of 55 displacing the Working point enables advantage to be taken of the aforesaid fact, namely that the highest modulation amplitudes do not occur simultaneously. The energy component which in the case of the greatest modulation amplitudes is available for each channel can be made higher than if a mean value of the carrier is continuously operative in each channel. Should nevertheless the maximum peaks of several channels happen to occur simultaneously then this will by no means be harmful since such a coincidence will only be momentary and because the arrangements here concerned, such as electron tubes, readily stand such momentary overloads.

In addition to the improvement in the energy relationships the advantage is obtained that the 1. In a high frequency transmitter wherein a high frequency oscillation is modulated by a plurality of intermediate carriers and wherein intermediate frequency devices having modulation characteristics are employed for controlling said carriers by a corresponding plurality of signal waves, the method which comprises fluctuating each of said devices about` mean AWorking points on its characteristic in accordance with the instantaneous magnitudes of its corresponding signal Wave to effect modulation of said carriers, and displacing the Working points along said characteristics in dependence on the average amplitudes of its corresponding signal Waves.

2. In a high frequency transmitter of the type in which a plurality of intermediate carriers are modulated by a corresponding plurality of signal Waves and are thereafter used to modulate a high frequency carrier, the method of modulating and controlling such an intermediate carrier which comprises fluctuating the amplitude of each of said intermediate carriers above and below a mean Working level in accordance with the instantaneous magnitude of the corresponding signal Wave, and displacing said mean Working level in dependence on the' average amplitude of its corresponding signal wave.

LEO PUNGS. 

